Field of the Invention
The present invention relates to an image forming apparatus that forms images on sheets based on image data and is capable of performing print recovery processing.
Description of the Related Art
In accordance with recent improvement of image forming apparatuses in processing speed and image quality, a printing method called POD (Print On Demand) has been realized in which digital data is directly printed without performing a plate making process and a machine plate-making process of the conventional offset printing.
The POD makes it possible to perform small-lot wide-variety printing, and shorten the time of delivery, whereby it is possible to reduce inventories. Further, to make it possible to handle various kinds of prints, there has been proposed means for making detailed settings, on a job-by-job basis, using a job ticket, such as a JDF (Job Definition Format) job ticket. Further, since various kinds of prints are handled, various qualities and reliabilities are required depending on the type of prints. For example, in the case of envelopes receiving postal mails, if the print quality is low, the postal mails cannot be delivered to correct addresses, and in the case of documents, such as certificates, if page duplication or page missing occurs, the reliability of documents is lost. Therefore, the quality is most important for these types of prints. On the other hand, for prints of the same contents, printed in large numbers, such as advertisement leaflets and in-house documents, importance is placed on costs and printing speeds rather than quality.
Incidentally, in the case of occurrence of an error, such as a sheet jam (paper jam) in which a sheet being conveyed is jammed in an image forming apparatus, printing is sometimes stopped. When printing is stopped, an operation for removing the sheet remaining within the apparatus is performed by a user, and normally, after removing the jammed sheet, recovery processing for automatically resuming the stopped print processing is performed (see Japanese Laid-Open Patent Publication (Kokai) No. H09-311770).
Recovery processing is realized by detecting a state of discharge of sheets at the time of occurrence of a sheet jam, using a sensor, and determining a page from which print processing is to be resumed. However, the position of the sensor is different depending on the apparatus, and hence it is not necessarily possible to resume print processing from the correct page, which sometimes causes page duplication or page missing. To solve this problem, there has been proposed a technique in which in the case of occurrence of a sheet jam, execution of a job suffering from the sheet jam is stopped, and printing is performed again from the first page of the job (see Japanese Laid-Open Patent Publication (Kokai) No. 2008-194849).